mei: fix the back to back interrupt handling

Since the newer HW sports two interrupts causes we cannot
just simply acknowledge the interrupts directly in the quick handler
and store the cause in the member variable, as the cause
will be overridden upon next interrupt while the interrupt thread
was not yet scheduled handling the previous interrupt.
The simple fix is to disable interrupts in quick handler
and acknowledge and enabled them in the interrupt thread.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>